1. Technical Field
The present invention relates to a magnetic transfer method and magnetic recording medium. More specifically, it relates to a magnetic transfer method whereby a servo signal or specific data for positioning a magnetic head which carries out a writing and reading of data written onto a magnetic recording medium in a hard disc drive (hereafter called an HDD) is written onto a magnetic recording medium using a magnetic transfer technique, and to a magnetic recording medium onto which transfer information is written using the magnetic transfer method.
2. Related Art
At present, the writing of magnetic information onto a magnetic recording medium is carried out in the following way. That is, after a magnetic recording medium in a condition in which no magnetic information is written thereon is set in an HDD device, necessary magnetic information is written into concentric areas with uniform widths on the magnetic recording medium, called tracks, inside the HDD.
The reading and writing of the data is carried out while a magnetic head moves along the tracks. At this time, the magnetic head detects a positional misalignment of the tracks by means of a magnetic signal, called a servo signal, written onto the magnetic recording medium, and is controlled so as not to deviate from the tracks.
In order to accurately write servo signals concentrically on a magnetic recording medium on which nothing is written, it is necessary to insert a device with a precise position control function from the exterior for every HDD, and several hours are needed to write several hundred thousand tracks onto one surface. Along with a recent improvement in recording density, a position control device of even higher precision, and a longer writing time, has become necessary, leading to a considerable disadvantage from the aspects of HDD productivity and cost.
Therefore, a technique and device have been developed with which, by bringing the transfer master with the servo signal pattern into close contact with a magnetic recording medium, and applying a magnetic field from the exterior, the servo signal pattern is instantaneously transferred to the magnetic recording medium. Because of this, it is possible to reduce the drive manufacturing cost and increase the track density (narrow the track width).
However, when attempting to bring the transfer master and magnetic recording medium, which are both smooth surfaces, into overall close contact at one time, the order in which the surfaces are brought into close contact, from the start to the finish of the bringing into close contact, is left to chance. Depending on the order, there arises a problem such as the air between the transfer surface and transfer receiving surface being trapped, and an “air accumulation” occurring, so that the transfer master and magnetic recording medium do not come into good close contact. The predetermined servo signal is not transferred to a place where the air is accumulated, and a missing signal error occurs.
Considering this situation, a method has been proposed whereby, for example, the transfer master and magnetic recording medium are brought into close contact inside a pressurizing chamber or inside a depressurizing chamber, in an attempt for a highly accurate, even close contact of the transfer master and magnetic recording medium (for example, refer to JP-A-2004-234710 and JP-A-2003-281715).
Also, there is also a proposal to provide an air escape groove or hole in the transfer master, and through this to bring the transfer master and magnetic recording medium into close contact by suctioning (for example, refer to JP-A-11-025455).
However, with the method described in JP-A-2004-234710, as a chamber of a thickness which can withstand the pressurization or depressurization necessary for an overall close contact, for example, a thickness of a few millimeters, is interposed between a magnetic field generating module and a conjoined body, there is a problem in that it is not possible to bring the magnetic field generating module close to the conjoined body, and the transfer signal strength decreases.
Also, in order to provide an air escape groove or hole in the transfer master, as in JP-A-11-025455, there is a need to make a precisely controlled microscopic form in the range of a few to a few hundred microns in the transfer master.
Therefore, a method has been proposed whereby the order of bringing into close contact is controlled by a linear pressurization with a roller, with no need for the above-described chamber structure, or making of a groove or hole in the transfer master (for example, refer to JP-A-61-063929).
Also, there is a proposal whereby, as a master such that both parties come into particularly close contact when a master including an information code and a magnetic disc are brought into close contact, the master is curved in such a way that, in a natural condition, the central portion of the surface of the master facing the magnetic disc approximates the magnetic disc (for example, refer to JP-A-11-161956). According to this proposal, it is possible to sequentially expand the contact area of the master and magnetic disc from the central portion to the external peripheral portion during the process of bringing the master and magnetic disc into close contact. With this approach it is possible to expel the air between the master and magnetic disc without it accumulating, and to therefore bring the master and magnetic disc into particularly close contact.
With the method described in JP-A-11-161956, in order to curve the master, a stress film with a high thermal expansion coefficient in comparison with that of a master substrate made of glass, silicon, or the like, is affixed to a master substrate at a temperature higher than room temperature, and furthermore, by making a slit in the master substrate, the bending rigidity of the master substrate is reduced, and the amount of deformation is increased.
With the method described in JP-A-61-063929, the area sandwiched and pressurized by the roller is brought evenly into close contact, but as soon as the roller passes, the close contact is released. As a magnetic field must be applied while the close contact condition is maintained, it follows that there is no freedom in the disposition of the roller and magnetic field generating module and, for example, in the event of installing a magnetic field generating module on both sides, or in the event of increasing the size of the magnetic field generating module in order to strengthen the magnetic field, the pressurization range of the roller becomes insufficient, with the result that a missing signal occurs.
The same problem applies also to the previously described JP-A-2004-234710 and JP-A-11-025455. That is, as it is necessary to bring the magnetic field generating module close with the pressurized or depressurized condition still maintained in order to carry out a magnetic transfer while maintaining an even, close contact condition, a way of maintaining close contact during the magnetic transfer is essential with either method.
With the method described in JP-A-11-161956, it being necessary to deposit a stress film so that it becomes a homogeneous film at a temperature higher than room temperature, the manufacture of the master is troublesome, and the cost increases. Also, as it curves at room temperature, and contains a slit, the master substrate is of low strength, is difficult to handle, and the like.